System for dynamically determining vehicle rear/trunk loading for use in a vehicle control system

ABSTRACT

A control system ( 18 ) and method for an automotive vehicle ( 10 ) includes a pitch rate sensor ( 37 ) generating a pitch rate signal, a longitudinal acceleration sensor ( 36 ) generating a longitudinal acceleration signal, and a yaw rate sensor ( 28 ) generating a yaw rate signal. A safety system ( 44 ) and the sensors are coupled to a controller. From the sensors, the controller ( 26 ) determines an added mass and a position of the added mass, a pitch gradient and/or a pitch acceleration coefficient that takes into account the added mass and position. The controller controls a vehicle system in response to the added mass and the position of the added mass, the pitch gradient and/or pitch acceleration coefficient variables.

CROSS REFERENCE

This application is a divisional of co-pending U.S. application Ser. No.11/010,863 filed on Dec. 13, 2004 herein incorporated by reference.

TECHNICAL FIELD

The present invention relates generally to a control apparatus forcontrolling a system of an automotive vehicle in response to senseddynamic behavior, and more specifically, to a method and apparatus fordetermining a rear vehicle loading and/or the impact of vehicle loadingon the control apparatus of the vehicle.

BACKGROUND

Recently, vehicle roll stability control (RSC) schemes, i.e., U.S. Pat.No. 6,324,446, have been proposed to address the issue offriction-induced rollovers. RSC system includes a variety of sensorssensing vehicle states and a controller that controls a distributedbrake pressure to reduce a tire force so the net moment of the vehicleis counter to the roll direction.

During an event causing the vehicle to roll, the vehicle body is subjectto a roll moment due to the coupling of the lateral tire force and thelateral acceleration applied to the center of gravity of vehicle body.This roll moment causes suspension height variation, which in turnresults in a vehicle relative roll angle (also called chassis roll angleor suspension roll angle). The relative roll angle is an importantvariable that is used as an input to the activation criteria and toconstruct the feedback pressure command, since it captures the relativeroll between the vehicle body and the axle. The sum of the chassis rollangle and the roll angle between wheel axle and the road surface (calledwheel departure angle) provides the roll angle between the vehicle bodyand the average road surface, which is one of the important variablesfeeding back to the roll stability control module. Trucks, SUVs and carssometimes are used for carrying heavy loads. For example, a truck fullof cargo is loaded in the rear, a trunk of a car may be loaded, and SUVor van may be loaded on its rear. The rear loading may cause the vehicleto have a pitch due to the increased load.

A large rear/trunk load (additional mass) may saturate the lateralforces on the rear axle of the vehicle, making the vehicle more prone tooversteer. In terms of stability, a GWAR (gross weight at rear axle) maycause the vehicle to move with a large side slip angle during someaggressive maneuvers. When the vehicle is sliding at a very largesideslip angle, it gets into nonlinear range of its vehicle dynamics,and sometimes the vehicle could be tripped and rolled over. It isusually hard for the ordinary driver to control and the vehicle dynamicscontrols have to be activated. Hence, it would be desirable to adjustcontrol authority in stability controls in order to achieve improvedperformance for a vehicle with large trunk or rear loading.

The large vehicle trunk loading may also have adverse effect on vehiclesensor readings. For example, the trunk loading could cause the vehiclepitch down towards its rear axle. Such loading-induced pitch may causeerroneous readings from a pitch rate sensor, a yaw rate sensor and alongitudinal acceleration sensor. Hence it is desirable to determinesuch loading-induced pitch misalignment based on the detected trunk orrear loading and to use this information to compensate the sensor signaloutputs. Such trunk loading induced pitch misalignment can also be usedto conduct vehicle body leveling control and to adjust the orientationof the headlights.

SUMMARY OF THE INVENTION

It is therefore one object of the invention to provide a system for acharacterization of the chassis pitch that may be used in conjunctionwith the various vehicle systems including but not limited to a rollstability control system, a yaw stability control, a headlight levelingcontrol and a vehicle leveling control. In the stability controls, suchtrunk loading can be used to determine accurate vehicle pitch trendingfor vehicles, and adaptively adjust the computation of the pitch angleand/or adaptively adjust the activation criteria for the stabilitycontrol system. More specifically, the present invention may determinean additional mass and position of the mass or the effect of theadditional mass and position. That is, a relatively small mass changemay significantly impact the directional dynamics of the vehicle. A rearor trunk load can affect the vehicle pitch dynamics and lateral dynamicsto increase the vehicle oversteer characteristics. The control systemthen can make a determination as to how to command the appropriateactuators in an increasing control sense to more aggressively correctthe potential unstable condition, or in a desensitizing sense to reducethe amount of actuation for correcting potential false activation.

In one aspect of the invention, a method of controlling a vehiclecomprises determining a pitch gradient and/or a pitch accelerationcoefficient. That is, the pitch gradient and the pitch accelerationcoefficient may be used individually or in combination to control avehicle system such as a safety system.

In a further aspect of the invention, a method of controlling a safetydevice for a vehicle comprises determining a composite parameter calledpitch gradient, determining another composite parameter called pitchacceleration coefficient, determining an added mass and a position ofthe added mass from the pitch gradient and the pitch accelerationcoefficient, and controlling the vehicle system in response to the addedmass and position.

In another aspect of the invention, a control system for an automotivevehicle includes a pitch rate sensor generating a pitch rate signal, alongitudinal acceleration sensor generating a longitudinal accelerationsignal, and a yaw rate sensor generating a yaw rate signal. A safetysystem and the sensors are coupled to a controller. The controllerdetermines an added mass and a position of the added mass from the rollrate, the longitudinal acceleration and the yaw rate and controls thesafety system in response to the added mass and position.

One advantage of the invention is that the vehicle trunk loadingcondition can be detected and determined very accurately. Such loadingconditions cannot be accurately detected through vehicle longitudinaldynamics as in some of the existing methods which use engine torque andthe vehicle longitudinal acceleration to compute the vehicle mass.

Other advantages and features of the present invention will becomeapparent when viewed in light of the detailed description of thepreferred embodiment when taken in conjunction with the attacheddrawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a vehicle with coordinate framesaccording to the present invention.

FIG. 2 is a block diagram of a stability system according to the presentinvention.

FIG. 3 is a front view of an automotive vehicle illustrating variousangles according to the present invention.

FIG. 4 is a side view of an automotive vehicle in a pitching conditionillustrating various variables thereon.

FIG. 5 is a top view of an automotive vehicle having variables used inthe following calculations thereon.

FIG. 6 is a detailed block diagrammatic view of a controller accordingto one embodiment of the present invention.

FIG. 7 is a flowchart of a method of operating the present invention.

DETAILED DESCRIPTION

In the following figures, the same reference numerals will be used toidentify the same components. The present invention may be used inconjunction with a rollover control system for a vehicle. The presentinvention may also be used with a deployment device such as airbag oractive roll bar or pre-tensioning belts. The present invention couldpass information to an adaptive cruise control system or a brake basedcollision avoidance system to change the brake request levels of thesystem. The present invention will be discussed below in terms ofpreferred embodiments relating to an automotive vehicle moving in athree-dimensional road terrain. The present invention is described withrespect to determining an added mass and position of the added mass.However, as will be described below the added mass and position may notbe directly determined, rather by adaptively updating a pitch conditionparameter such as a pitch gradient value and/or a pitch accelerationcoefficient, the effects of added mass and the position of the addedmass may be included in those values. Such values may also be referredto as an “adaptive” pitch gradient and an “adaptive” pitch accelerationcoefficient. The various pitch parameters may be referred to asadaptively determined meaning that such values may change due to changesin the mass or load over time. That is, such values are not fixed. Thatis the values may be updated as the vehicle is running or driving. Thevalues may then be averaged.

It should also be noted that while one of the pitch gradient or pitchacceleration coefficient may be adaptively determined, the other twovalues may not be adaptive.

Referring to FIG. 1, an automotive vehicle 10 with a safety system ofthe present invention is illustrated with the various forces and momentsthereon during a dynamic condition. Vehicle 10 has front right (FR) andfront left (FL) wheel/tires 12A and 12B and rear right (RR) wheel/tires13A and rear left (RL) wheel/tires 13B respectively. The vehicle 10 mayalso have a number of different types of front steering systems 14 a andrear steering systems 14 b, including having each of the front and rearwheels configured with a respective controllable actuator, the front andrear wheels having a conventional type system in which both of the frontwheels are controlled together and both of the rear wheels arecontrolled together, a system having conventional front steering andindependently controllable rear steering for each of the wheels, or viceversa. Generally, the vehicle has a weight represented as Mg at thecenter of gravity of the vehicle, where g=9.8 m/s² and M is the totalmass of the vehicle.

As mentioned above, the system may also be used with safety systemsincluding active/semi-active suspension systems, anti-roll bar, orairbags or other safety devices deployed or activated upon sensingpredetermined dynamic conditions of the vehicle.

The sensing system 16 is coupled to a control system 18. The sensingsystem 16 may comprise many different sensors including the sensor settypically found in a roll stability control or a rollover control system(including lateral accelerometer, yaw rate sensor, steering angle sensorand wheel speed sensor which are equipped for a traditional yawstability control system) together with a roll rate sensor and alongitudinal accelerometer. The various sensors will be furtherdescribed below. The sensors may also be used by the control system invarious determinations such as to determine a lifting event, determine aposition of a mass, etc. The wheel speed sensors 20 are mounted at eachcorner of the vehicle and generate signals corresponding to therotational speed of each wheel. The rest of the sensors of sensingsystem 16 may be mounted directly on the center of gravity of thevehicle body, along the directions x,y and z shown in FIG. 1. As thoseskilled in the art will recognize, the frame from b₁,b₂ and b₃ is calleda body frame 22, whose origin is located at the center of gravity of thecar body, with the b₁ corresponding to the x axis pointing forward, b₂corresponding to the y axis pointing off the driving side (to the left),and the b₃ corresponding to the z axis pointing upward. The angularrates of the car body are denoted about their respective axes as ω_(x)for the roll rate, ω_(y) for the pitch rate and ω_(z) for the yaw rate.Calculations may take place in an inertial frame 24 that may be derivedfrom the body frame 22 as described below.

The angular rate sensors and the accelerometers may be mounted on thevehicle car body along the body frame directions b₁,b₂ and b₃ which arethe x-y-z axes of the sprung mass of the vehicle.

The longitudinal acceleration sensor is mounted on the car body locatedat the center of gravity, with its sensing direction along b₁-axis,whose output is denoted as a_(x). The lateral acceleration sensor ismounted on the car body located at the center of gravity, with itssensing direction along b₂-axis, whose output is denoted as a_(y).

The other frame used in the following discussion includes the roadframe, as depicted in FIG. 1. The road frame system r₁r₂r₃ is fixed onthe driven road surface, where the r₃ axis is along the average roadnormal direction computed from the normal directions of thefour-tire/road contact patches.

In the following discussion, the Euler angles of the body frame b₁b₂b₃with respect to the road frame r₁r₂r₃ are denoted as θ_(xbr) andθ_(ybr), which are also called the relative Euler angles (i.e., relativeroll and relative pitch angles, respectively).

Referring now to FIG. 2, roll stability control system 18 is illustratedin further detail having a controller 26 used for receiving informationfrom a number of sensors which may include a yaw rate sensor 28, a speedsensor 20, a lateral acceleration sensor 32, a vertical accelerometersensor 33, a roll angular rate sensor 34, a steering wheel (hand wheel)angle sensor 35, a longitudinal acceleration sensor 36, a pitch ratesensor 37, steering angle (of the wheels or actuator) position sensor38, suspension load sensor 40 and suspension position sensor 42. Itshould be noted that various combinations and sub-combinations of thesensors may be used.

Speed sensor 20 may be one of a variety of speed sensors known to thoseskilled in the art. For example, a suitable speed sensor may include asensor at every wheel that is averaged by controller 26. The controllermay translate the wheel speeds into the speed of the vehicle. Yaw rate,steering angle, wheel speed and possibly a slip angle estimate at eachwheel may be translated back to the speed of the vehicle at the centerof gravity. Various other algorithms are known to those skilled in theart. Speed may also be obtained from a transmission sensor. For example,if speed is determined while speeding up or braking around a corner, thelowest or highest wheel speed may not be used because of its error.Also, a transmission sensor may be used to determine vehicle speed.

Roll angular rate sensor 34 and pitch rate sensor 37 may sense the rollcondition or lifting of the vehicle based on sensing the height of oneor more points on the vehicle relative to the road surface. Sensors thatmay be used to achieve this include but are not limited to a radar-basedproximity sensor, a laser-based proximity sensor and a sonar-basedproximity sensor. The roll rate sensor 34 may also use a combination ofsensors such as proximity sensors to make a roll rate determination.

Roll rate sensor 34 and pitch rate sensor 37 may also sense the rollcondition or lifting based on sensing the linear or rotational relativedisplacement or displacement velocity of one or more of the suspensionchassis components. This may be in addition to or in combination withsuspension position sensor 42. The position sensor 42, roll rate sensor34 and/or the pitch rate sensor 37 may include a linear height or travelsensor, a rotary height or travel sensor, a wheel speed sensor used tolook for a change in velocity, a steering wheel position sensor, asteering wheel velocity sensor and a driver heading command input froman electronic component that may include steer by wire using a handwheel or joy stick.

The roll condition or lifting may also be sensed by sensing directly orestimating the force or torque associated with the loading condition ofone or more suspension or chassis components including a pressuretransducer in an act of air suspension, a shock absorber sensor such asa load sensor 40, a strain gauge, the steering system absolute orrelative motor load, the steering system pressure of the hydrauliclines, a tire laterally force sensor or sensors, a longitudinal tireforce sensor, a vertical tire force sensor or a tire sidewall torsionsensor. The yaw rate sensor 28, the roll rate sensor 34, the lateralacceleration sensor 32, and the longitudinal acceleration sensor 36 maybe used together to determine that the wheel has lifted. Such sensorsmay be used to determine wheel lift or estimate normal loadingassociated with wheel lift. These are passive methods as well.

The roll condition of the vehicle may also be established by one or moreof the following translational or rotational positions, velocities oraccelerations of the vehicle including a roll gyro, the roll rate sensor34, the yaw rate sensor 28, the lateral acceleration sensor 32, thevertical acceleration sensor 33, a vehicle longitudinal accelerationsensor 36, lateral or vertical speed sensor including a wheel-basedspeed sensor 20, a radar-based speed sensor, a sonar-based speed sensor,a laser-based speed sensor or an optical-based speed sensor.

In the preferred embodiment, the sensors are located at the center ofgravity of the vehicle. Those skilled in the art will recognize that thesensor may also be located off the center of gravity and translatedequivalently thereto.

Lateral acceleration, roll orientation and speed may be obtained using aglobal positioning system (GPS). Based upon inputs from the sensors,controller 26 may control a safety device 44. Depending on the desiredsensitivity of the system and various other factors, not all the sensors28-42 may be used in a commercial embodiment.

Load sensor 40 may be a load cell coupled to one or more suspensioncomponents. By measuring the stress, strain or weight on the load sensora shifting of the load can be determined.

Controller 26 may include a signal multiplexer 50 that is used toreceive the signals from the sensors 28-42. The signal multiplexer 50provides the signals to a wheel lift detector 52, a vehicle roll anglecalculator 54, and to a roll stability control (RSC) feedback controlcommand 56. Also, wheel lift detector 52 may be coupled to the vehicleroll angle calculator 54. The vehicle roll angle calculator 54 may alsobe coupled to the RSC feedback command 56. The RSC feedback command 56may include a torque controller 57. Vehicle roll angle calculator 54 isdescribed in U.S. Provisional Applications 60/400,376 and 60/400,172,and in U.S. patent application Ser. No. 10/459,697, the disclosures ofwhich are incorporated herein by reference.

A loading detector 58 may also be included in controller 26. The loadingdetector 58 may be used to determine an additional mass of the vehicleand a position or longitudinal distance of the mass as will be describedbelow.

Safety device 44 may control an airbag 45 or a steering actuator 46A-46at one or more of the wheels 12A, 12B, 13A, 13B of the vehicle. Also,other vehicle components such as a suspension control 48 may be used toadjust the suspension to prevent rollover.

Safety device 44 may control the position of the front right wheelactuator 46A, the front left wheel actuator 46B, the rear left wheelactuator 46C, and the right rear wheel actuator 46D. Although asdescribed above, two or more of the actuators may be simultaneouslycontrolled. For example, in a rack-and-pinion system, the two wheelscoupled thereto are simultaneously controlled. Based on the inputs fromsensors 28 through 42, controller 26 determines a roll condition and/orwheel lift and controls the steering position and/or braking of thewheels.

Safety device 44 may be coupled to a brake controller 60. Brakecontroller 60 controls the amount of brake torque at a front right brake62A, front left brake 62 b, rear left brake 62 c and a rear right brake62 d. Other safety systems such as an antilock brake system 64, a yawstability control system 66 and a traction control system 68 may alsobenefit from the knowledge of the pitch gradient, the pitch accelerationcoefficient, additional mass and position of the mass. This informationmay impact the control strategy such as an amount of braking may bemodified.

The output of the controller may be coupled to a vehicle body levelingsystem 70, a headlight adjustment system 72 and a sensor signalcompensation block 74. The body leveling system 70 may be coupled tosuspension control 48 which control the suspension to compensate for thechange in the pitch angle due to added mass. The headlight aimingdirection may also be changed with headlight adjustment block 72.Various sensor signals may be changed by a factor due to the inducedpitch misalignment.

The roll condition is one condition that may be sensed and modified dueto additional load. The roll condition of a vehicle can be characterizedby the relative roll angle between the vehicle body and the wheel axleand the wheel departure angle (between the wheel axle and the averageroad surface). Both the relative roll angle and the wheel departureangle may be calculated in relative roll angle estimation module byusing the roll rate and lateral acceleration sensor signals. If both therelative roll angle and the wheel departure angles are large enough, thevehicle may be in either single wheel lifting or double wheel lifting.On the other hand, if the magnitude of both angles is small enough, thewheels are likely all grounded. In the case that both of them are notsmall and the double wheel lifting condition is detected or determined,the sum of those two angles will be used by the feedback control moduleto compute the desired actuation command for achieving rollover controlperformance.

The roll condition of a vehicle can be characterized by rollingradius-based wheel departure roll angle, which captures the anglebetween the wheel axle and the average road surface through the dynamicrolling radii of the left and right wheels when both of the wheels aregrounded. Since the computation of the rolling radius is related to thewheel speed and the linear velocity of the wheel, such rolling-radiusbased wheel departure angle will assume abnormal values when there arelarge wheel slips. This happens when a wheel is lifted and there istorque applied to the wheel. Therefore, if this rolling radius-basedwheel departure angle is increasing rapidly, the vehicle might havelifted wheels. Small magnitude of this angle indicates the wheels areall grounded.

The roll condition of the vehicle can be seen indirectly from the wheellongitudinal slip. If during a normal braking or driving torque thewheels at one side of the vehicle experience increased magnitude ofslip, then the wheels of that side are losing longitudinal road torque.This implies that the wheels are either driven on a low mu surface orlifted up. The low mu surface condition and wheel-lifted-up conditioncan be further differentiated based on the chassis roll anglecomputation, i.e., in low mu surface, the chassis roll angle is usuallyvery small. Hence, an accurate determination of chassis roll is desired.

The roll condition of the vehicle can be characterized by the normalloading sustained at each wheel. Theoretically, when a normal loading ata wheel decreases to zero, the wheel is no longer contacting the roadsurface. In this case a potential rollover is underway. Large magnitudeof this loading indicates that the wheel is grounded. Normal loading isa function of the calculated chassis roll and pitch angles. Hence, anaccurate determination of chassis roll and pitch angles is desired.

The roll condition can be identified by checking the actual road torquesapplied to the wheels and the road torques, which are needed to sustainthe wheels when they are grounded. The actual road torques can beobtained through torque balancing for each wheel using wheelacceleration, driving torque and braking torque. If the wheel iscontacting the road surface, the calculated actual road torques mustmatch or be larger than the torques determined from the nonlineartorques calculated from the normal loading and the longitudinal slip ateach wheel.

The roll condition of a vehicle can be characterized by the chassis rollangle itself, i.e., the relative roll angle θ_(xr) between the vehiclebody and the wheel axle. If this chassis roll angle is increasingrapidly, the vehicle might be on the edge of wheel lifting or rollover.Small magnitude of this angle indicates the wheels are not lifted or areall grounded. Hence, an accurate determination of the chassis roll angleis beneficial for determining if the vehicle is in non-rollover events.

The roll condition of a vehicle can also be characterized by the rollangle between the wheel axle and the average road surface, this iscalled wheel departure angle. If the roll angle is increasing rapidly,the vehicle has lifted wheel or wheels and aggressive control actionneeds to be taken in order to prevent the vehicle from rolling over.Small magnitude of this angle indicates the wheels are not lifted.

The center of gravity C is also illustrated with nominal mass M. A rollaxis is also illustrated at a distance D from the center of gravity.a_(y) is the lateral acceleration.

Referring now to FIG. 3, the relationship of the various angles of thevehicle 10 relative to the road surface 11 is illustrated. In thefollowing, a reference road bank angle θ_(bank) is shown relative to thevehicle 10 on a road surface. The vehicle has a vehicle body 10 a andwheel axle 10 b. The wheel departure θ_(wda) is the angle between thewheel axle and the road. The relative roll angle θ_(xr) is the anglebetween the wheel axle 10 b and the body 10 a. The global roll angleθ_(x) is the angle between the horizontal plane (e.g., at sea level) andthe vehicle body 10 a.

Another angle of importance is the linear bank angle. The linear bankangle is a bank angle that is calculated more frequently (perhaps inevery loop) by subtracting the relative roll angle generated from alinear roll dynamics of a vehicle (see U.S. Pat. No. 6,556,908 which isincorporated by reference herein), from the calculated global roll andpitch angles (as the one in U.S. patent application Ser. No. 09/789,656,which is incorporated by reference herein). If all things were slowlychanging without drifts, errors or the like, the linear bank angle andreference road bank angle terms would be equivalent.

Referring now to FIGS. 4 and 5, an automotive vehicle 10 is illustratedwith various parameters illustrated thereon. A change in mass ΔM isillustrated relative to nominal center of gravity C₀. The center ofgravity moves to C when the added mass ΔM is added thereto. The changein mass or load ΔM is positioned at a distance H above the load floor80. The nominal center of gravity C₀ is located a distance L from theadded mass in longitudinal direction. The longitudinal distance betweenthe new center of gravity and the nominal center of gravity C₀ is ΔL.

In FIG. 5, the longitudinal acceleration is denoted by a_(x) whereas thelongitudinal velocity is denoted v_(x). The lateral acceleration andlateral velocity is denoted by a_(y),v_(y) respectively. The steeringwheel angle is denoted by δ_(w). The wheelbase of the vehicle is denotedby the symbol b.

Referring now to FIG. 6, controller 26 is illustrated in further detail.Controller 26 receives the various sensor signals, for example, thepitch rate, longitudinal acceleration, and yaw rate from the respectivesensor signals. Other input signals such as the relative roll angle,flatness index and vehicle motion characteristics may be determined fromother various sensor signals or from a stability control system such asa roll stability control system. The flatness index provides anindication as to the flatness (pitch/bank) of the road. One way todetermine a flatness index is set forth in U.S. Pat. No. 6,178,248,which is incorporated by reference herein. Vehicle motioncharacteristics may, for example, provide an indication of the motion ofthe vehicle such as acceleration or deceleration. From the sensorsignals, the loading position in a longitudinal direction and amount ofloading, and the pitch gradient and pitch acceleration coefficient maybe determined. These values may ultimately generate a vehicle pitchangle compensation term, which can be used for correcting sensor signalsand for a roll stability control system to adjust control gains andthresholds. Instead of directly determining the load and position of theload, an adaptive pitch acceleration coefficient and an adaptive pitchgradient may be determined first. Such parameters inherently relate tothe load and position of the load included therein. Therefore they canbe used to find the loading and the loading position. As will be furtherdescribed below, the controller 26 uses the pitch rate signal andperforms a derivative in box 84 to generate the pitch accelerationsignal {dot over (ω)}_(y), which is then filtered by the first filter 86to generate the variable X. The X value is provided to the pitchgradient and pitch acceleration coefficient determination module 88. Thelongitudinal acceleration signal is filtered in the second filter 90 andprovided to the pitch gradient and pitch acceleration coefficientdetermination module 88 illustrated as Y. The pitch rate, yaw rate andrelative roll angle are provided to a Z determination module 92 todetermine the intermediate variable Z. The intermediate variable Z isfiltered in the third filter number 94 and provided to pitch gradientand pitch acceleration coefficient determination module 88. As will befurther described below, the output of the pitch gradient and pitchacceleration coefficient determination module 88 is the pitch gradientand the pitch acceleration coefficient which are provided to aloading/loading position detection block 96. The loading/loadingposition detection block 96 generates a change in mass, a positionsignal and a change in position signal corresponding to a change in thecenter of gravity of the vehicle. A vehicle loading compensation term isgenerated in loading characterization block 98. The output of theloading characterization block 98, may be provided to a stabilitycontrol module and/or a loading induced pitch misalignment module. Theloading induced pitch misalignment may be used by the vehicle bodyleveling system 70, the headlight adjustment system 72 and the sensorsignal compensation block 74.

Referring now to FIG. 7, the operation of the controller 26 is describedin further detail. In step 102, the various sensors such as the pitchrate sensor, the longitudinal acceleration sensor, and yaw rate sensorare read. In step 103, the pitch gradient and pitch accelerationcoefficient are determined.

There are two pitch angle computations set forth below. Ultimately apitch gradient and a pitch acceleration coefficient are derived from therelative pitch angle and the other the global pitch angle. The relativepitch angle σ_(relative) is a function of the longitudinal accelerationa_(x), the pitch acceleration {dot over (ω)}_(y), the pitch gradient ρand the pitch acceleration coefficient σ

σ_(relative) =f(a _(x),{dot over (ω)}_(y);ρ,σ)  (1)

In z-transformation,

σ_(relative) =ρT _(pitch)(z)a _(x) −σT _(pitch)(z){dot over(ω)}_(y)  (2)

where

$\left\{ {\quad\begin{matrix}{H = {h + \frac{B}{2\; A} + \sqrt{{\frac{1}{4}\left( \frac{B}{A} \right)^{2}} + {h\left( \frac{B}{A} \right)} + \left( \frac{B}{M_{s}} \right)^{2}}}} \\{{\Delta \; M} = \frac{\alpha}{h + \frac{B}{2\; \alpha} + \sqrt{{\frac{1}{4}\left( \frac{B}{A} \right)^{2}} + {h\left( \frac{B}{A} \right)} + \left( \frac{B}{M_{s}} \right)^{2}}}}\end{matrix}} \right.$

is a filter which reflects the linear pitch model of the vehicle. Noticethat during deceleration and acceleration, vehicle pitch motion behavesdifferently. In this case,

$\left\{ {\quad\begin{matrix}{H = {h + {\frac{B}{2\; A}\sqrt{{\frac{1}{4}\left( \frac{B}{A} \right)^{2}} + {h\left( \frac{B}{A} \right)} + \left( \frac{B}{M_{s}} \right)^{2}}}}} \\{{\Delta \; M} = \frac{\alpha}{h + \frac{B}{2\; \alpha} + \sqrt{{\frac{1}{4}\left( \frac{B}{A} \right)^{2}} + {h\left( \frac{B}{A} \right)} + \left( \frac{B}{M_{s}} \right)^{2}}}}\end{matrix}} \right.$

should be tuned differently for deceleration and acceleration. Denotethe pitch transfer function as T_(pitch) _(—) _(acc)(z) during vehicleacceleration, and as T_(pitch) _(—) _(dec)(z) during vehicledeceleration. Similarly the pitch gradient and the pitch accelerationcoefficient are different for the vehicle acceleration and decelerationand they are denoted as ρ^(acc) and σ^(acc) for acceleration, andρ^(dec) and σ^(dec) for deceleration.

On level ground, the global pitch angle φ_(global) is a function of thepitch rate ω_(y), the yaw rate ω_(z), relative roll angle θ_(relative)and the relative pitch angle θ_(relative)

φ_(global) =g(ω_(y),ω_(z),θ_(relative),φ_(relative))  (3)

In z-transformation,

φ_(global) =T _(adi)(z)[ω_(y)−ω_(z)θ_(relative) ]+T_(ssc)(z)φ_(relative)  (4)

where T_(adi)(z) and T_(ssc)(z) are two filters to conduct anti-driftintegration and steady state compensation. Notice that on level ground,the relative pitch angle and the global pitch angle are equal. Thereforefrom (1) and (3) or (2) and (4), relationships between the pitchgradient ρ and the pitch acceleration coefficient σ may be determined.Inserting (2) into (4) during acceleration,

φ_(global) =T _(adi)(z)[ω_(y)−ω_(z)θ_(relative)]+ρ^(acc) T _(ssc)(z)T_(pitch) _(—) _(acc)(z)a _(x)−σ^(acc) T _(scc)(z)T _(pitch) _(—)_(acc)(z){dot over (ω)}_(z)  (5)

or the following for deceleration

φ_(global) =T _(adi)(z)[ω_(y)−ω_(Z)θ_(relative)]+ρ^(dec) T _(ssc)(z)T_(pitch) _(—) _(dec)(z)a _(x)−σ^(dec) T _(ssc)(z)T _(pitch) _(—)_(dec)(z){dot over (ω)}_(z)  (6)

By equating (2) and (5) for vehicle acceleration case, the followingequation may be obtained

ρ^(acc) X ^(acc)−σ^(acc) Y ^(acc) =U  (7)

where

X ^(acc) =T _(ssc)(z)[T _(pitch) _(—) _(acc)(z)−1]a _(x)

Y ^(acc) =T _(ssc)(z)[T _(pitch) _(—) _(acc)(z)−1]{dot over(ω)}_(y)  (8)

and U is computed as the following

U=T _(adi)(z)[ω_(y)−ω_(z)θ_(relative)]  (9)

Similarly, by equating (2) and (6) for vehicle deceleration case, thefollowing equation may be obtained

ρ^(dec) X ^(dec)−σ^(dec) Y ^(dec) =U  (10)

where

X ^(dec) T _(ssc)(z)[T _(pitch) _(—) _(dec() z)−1]a _(x)

Y ^(dec) =T _(ssc)(z)[T _(pitch) _(—) _(dec)(z)−1]{dot over(ω)}_(y)  (11)

The following is a summary of the computation algorithm.

In step 104, the filtered longitudinal acceleration X is determined inthe following iterative equation

X _(k) =d _(x1) X _(k−1) +d _(x2) X _(k−2) +d _(x3) X _(k−3) +n _(x1) a_(x) _(k) +n _(x2) a _(x) _(k−1) +n _(x3) a _(k−2)  (12)

where d_(x) _(i) n_(x) _(i) are the involved filter coefficients. Noticethat, the above computation is good for both acceleration anddeceleration, and the deceleration value is denoted as X^(dec) and theacceleration value is denoted as X^(acc) with different sets of filtercoefficients. When the vehicle longitudinal acceleration signals a_(x)is changing from a positive value to a negative value and crossing zerovalue at the time instant k, the following reset is used to start thecomputation for X^(dec)

X _(k−1) ^(dec) =X _(k−1) ^(acc)

X _(k−2) ^(dec) =X _(k−2) ^(acc)

X _(k−3) ^(dec) =X _(k−3) ^(acc)  (13)

and the computation for X^(acc) is stopped. Similarly, when thevehicle's longitudinal acceleration signal a_(x) is changing from anegative value to a positive value and crossing zero value at the timeinstant t, the following reset is used to start the computation forX^(acc)

X _(t−1) ^(acc) =X _(t−1) ^(dec)

X _(t−2) ^(acc) =X _(t−2) ^(dec)

X _(t−3) ^(acc) =X _(t−3) ^(dec)  (14)

and the computation for X^(dec) is stopped.

In step 106, the filtered pitch acceleration Y is determined in thefollowing iterative equation

Y=d _(x1) Y _(k−1) +d _(x2) Y _(k−2) +d _(x3) Y _(k−3) +n _(x1){dot over(ω)}_(y) _(k) +n _(x2){dot over (ω)}_(y) _(k−1) +n _(x3){dot over(ω)}_(y) _(k−2)   (15)

Notice that the above computation is good for both acceleration anddeceleration, and the corresponding values are denoted as Y^(dec) andY^(acc) respectively with different sets of filter coefficients. Thesimilar reset schemes such as those in (13) and (14) for X^(dec) andX^(acc) are also used here.

In step 108, the filtered value U is determined in (9) as

U _(k) =d _(u) ₀ U _(k) +d _(u) ₁ U _(k−1) +d _(u) ₂ U _(k−2) +n _(u) ₀Z _(k) +n _(u) ₁ Z _(k−1) +n _(u) ₂ Z _(k−2)  (16)

where

Z _(k)=ω_(y) _(k) −ω_(z) _(k) θ_(relative) _(k)   (17)

where d_(ui),n_(ui) for i=1,2,3,4 are the involved 2^(nd) set of filtercoefficients.

Using the calculated value variables X_(k) ^(acc) Y_(k) ^(acc) at eachsampling instant k (during vehicle acceleration), or the calculatedvalue X_(t) ^(dec),Y_(t) ^(dec) at each sampling instant t (duringvehicle deceleration), U_(k) and U_(t), equation (7) and (10) can beused to potentially compute the unknown parameters of the pitch gradientρ^(acc) and ρ^(dec) the pitch acceleration coefficient σ^(acc) andσ^(dec).

Since equations (7) and (10) are true when the vehicle is driven onlevel ground and the vehicle does not have any wheel in the air (4 tiresare contacting the road), a conditional least-square (CLS) method can beused. Two CLS's may be used. The first CLS method conduct ρ^(acc) orρ^(dec) and σ^(acc) or σ^(dec) parameter updating after a fixed numberof conditional samples, while the second method updates ρ^(acc) orρ^(dec) and σ^(acc) or σ^(dec), and resets a covariance matrix at eachconditional sample.

Since ρ^(acc) or ρ^(dec) and σ^(acc) or σ^(dec) are related to theinertia parameters of the pitch motion of the vehicle body, only if thevehicle pitch mode is fully excited they can be identified correctlythrough least-square methods. The brake actions either from a driverbrake request or controlled brake request through a stability controlsystem can be used as such an excitation source. The same is true forvehicle throttling. However, under the steady-state driving condition(coasting) or vehicle acceleration/deceleration is smaller than athreshold, the least-square identification is not conducted. Consideringthe driver steering input could induce both roll and pitch dynamics(sharp turn causes vehicle weight towards the front), hence the steeringwheel angle velocity could be also used for identifying conditions forpitch mode excitation

δ_(wv min)≦|{dot over (δ)}_(w)|≦δ_(wv max) and |δ_(w)|≧δ_(w min)  (18)

where δ_(w) is the measured steering wheel angle, δ_(wv min) andδ_(wv max) are two thresholds to bound the magnitude of the steeringangle velocity. δ_(w min), is a threshold for bounding the magnitude ofthe steering wheel angle. The reason we actually limit the upper boundof the steering wheel angle velocity is due to the consideration thatextremely fast steering input could generate unrealistic dynamics.

In step 110, the conditional sum of the products or cross products ofthe above filtered variables are determined over a significant largenumber N of the conditional samples. This is performed using thefollowing iterative algorithm if the first CLS method is used

$\begin{matrix}{{{if}\mspace{14mu} \left( {{{{{\left( {a_{x} \geq {a_{xmin}\mspace{45mu} {or}\mspace{14mu} \left( {{{{{{{a_{x} \geq 0}\mspace{14mu}\&}\mspace{14mu} \delta_{wvmin}} \leq {{\overset{.}{\delta}}_{w}} \leq \delta_{wvmax}}\&}{\delta_{w}}} \leq \delta_{wmax}} \right)}} \right)\mspace{31mu}\&}\mspace{14mu} {level}\mspace{14mu} {ground}}\mspace{34mu}\&}\mspace{14mu} s} \leq N} \right)}\left\{ \mspace{14mu} {a_{11_{s + 1}^{acc}} = {{a_{11_{s}}^{acc} + {\left( X_{k}^{acc} \right)^{2}\mspace{14mu} a_{21_{s + 1}}^{acc}}} = {{a_{21_{s}}^{acc} - {X_{k}^{acc}Y_{k}^{acc}\mspace{14mu} a_{22_{s + 1}}^{acc}}} = {{a_{22_{s}}^{acc} + {\left( Y_{k}^{acc} \right)^{2}\mspace{14mu} b_{1_{s + 1}}^{acc}}} = {{b_{1_{s}}^{acc} + {X_{k}^{acc}U_{k}\mspace{14mu} b_{2_{s + 1}}^{acc}}} = {{b_{2_{s}}^{acc} - {Y_{k}^{acc}U_{k}\mspace{14mu} s}} = {s + 1}}}}}}} \right\}} & (19)\end{matrix}$

When the vehicle is decelerated

$\begin{matrix}{{{if}\mspace{14mu} \left( {{{{{\left( {a_{x} \leq {{- a_{xmin}}\mspace{45mu} {or}\mspace{14mu} \left( {{{{{{{a_{x} \leq 0}\mspace{14mu}\&}\mspace{14mu} \delta_{wvmin}} \leq {{\overset{.}{\delta}}_{w}} \leq \delta_{wvmax}}\&}{\delta_{w}}} \leq \delta_{wmax}} \right)}} \right)\mspace{31mu}\&}\mspace{14mu} {level}\mspace{14mu} {ground}}\mspace{34mu}\&}\mspace{14mu} s} \leq N} \right)}\left\{ \mspace{14mu} {a_{11_{s + 1}}^{dec} = {{a_{11_{s}}^{dec} + {\left( X_{t}^{dec} \right)^{2}\mspace{14mu} a_{21_{s + 1}}^{dec}}} = {{a_{21_{s}}^{dec} - {X_{t}^{dec}Y_{t}^{dec}\mspace{14mu} a_{22_{s + 1}}^{dec}}} = {{a_{22_{s}}^{dec} + {\left( Y_{t}^{dec} \right)^{2}\mspace{14mu} b_{1_{s + 1}}^{dec}}} = {{b_{1_{s}}^{dec} + {X_{t}^{dec}U_{k}\mspace{14mu} b_{2_{s + 1}}^{dec}}} = {{b_{2_{s}}^{dec} - {Y_{t}^{dec}U_{k}\mspace{14mu} s}} = {s + 1}}}}}}} \right\}} & (20)\end{matrix}$

Notice that the time instant denoted by k and t is different from theCLS updating instant denoted by s. Only if the conditions are satisfiedall the time, then s=k and t. N in (19) and (20) is the total number ofconditional samples used for the CLS, which could have value ranged from1000 to 80,000.

Step 110 is performed for the conditional sample when the road is alevel ground. The level ground can be identified if there is anindication that the vehicle is not on a significantly banked road.Therefore, checking the road bank angle can be used for this purpose forexample, using the method disclosed in U.S. Pat. No. 6,718,248. Thelevel of the ground can also be checked through a flatness index (as inthe one calculated in U.S. Pat. No. 6,718,248), or a road profiledetection (see U.S. Pat. No. 6,718,248), or a rough comparison betweenthe global roll angle and the nominal chassis roll angle.

In step 112, the pitch gradient and pitch acceleration coefficient arecalculated. ρ^(acc) and σ^(acc) are computed as in the following

$\begin{matrix}{{{{if}\mspace{14mu} s} = N}\left\{ \mspace{14mu} {{D^{acc} = {\min\left( {{\max\left( {{a_{11_{N}}^{acc} - \frac{\left( a_{21_{N}}^{acc} \right)^{2}}{\max\left( {a_{22_{N}}^{acc},a_{\min}} \right)}},{- a_{\min}}} \right)},a_{\min}} \right)}};\mspace{14mu} {\rho^{acc} = {\min\left( {{\max\left( {{\left( {b_{1_{N}} - \frac{a_{21_{N}}^{acc}b_{2_{N}}^{acc}}{\max \left( {a_{22_{N}},a_{\min}} \right)}} \right)\frac{1}{D^{acc}}},{\underset{\_}{\rho}}^{acc}} \right)},{\overset{\_}{\rho}}^{acc}} \right)}};\mspace{14mu} {\sigma^{acc} = {\min \left( {{\max \left( {{\begin{pmatrix}{\frac{a_{11_{N}}^{acc}b_{2_{N}}^{acc}}{\max\left( {a_{22_{N}}^{acc},a_{\min}} \right)} -} \\\frac{a_{21_{N}}^{acc}b_{1_{N}}^{acc}}{\max\left( {a_{22_{N}}^{acc},a_{\min}} \right)}\end{pmatrix}\frac{1}{D^{acc}}},{\underset{\_}{\sigma}}^{acc}} \right)},{\overset{\_}{\sigma}}^{acc}} \right)}};\mspace{14mu} {s = 0};\mspace{14mu} {a_{11_{s}}^{acc} = 0};{a_{21_{s}}^{acc} = 0};{a_{22_{s}}^{acc} = 0};\mspace{14mu} {b_{1_{s}}^{acc} = 0};{b_{2_{s}}^{acc} = 0};} \right\}} & (21)\end{matrix}$

where a_(min) is a small number (for example, 0.0001), which is used toremove division by zero in the implemented computation; ρ ^(acc) and ρ^(acc) are the respective lower and upper bounds of the pitch gradient,which can be calculated as

ρ ^(acc)=ρ₀ ^(acc)−Δρ

ρ ^(acc)=ρ₀ ^(acc)+Δρ  (22)

and ρ₀ ^(acc) is the nominal value of the pitch gradient (obtainedthrough vehicle testing for the vehicle with nominal loading), Δρ is theallowed variation of the pitch gradient; σ ^(acc) and σ ^(acc) are therespective lower and upper bounds of the pitch acceleration coefficient,which can be obtained as

σ ^(acc)=σ₀ ^(acc)−Δσ

σ ^(acc)=σ₀ ^(acc)+Δσ  (23)

and σ₀ ^(acc) is the nominal value of the pitch acceleration coefficient(for vehicle with nominal loading), Δσ is the allowed variation of thepitch acceleration coefficient. Similarly, the deceleration computationcan be conducted.

If the second CLS method is used, the pitch gradient ρ and the pitchacceleration coefficient σ can be calculated in through the followingiterative algorithm. First, during vehicle acceleration, a 2 by 2 matrixvariable V_(s+1) at the (s+1)th conditional time instant is calculatedfrom its past value V_(s) and the calculated filtered values of X_(k)^(acc) and Y_(k) ^(acc) as in the following

$\begin{matrix}{{{if}\mspace{14mu} \left( {{{{{\left( {a_{x} \geq {a_{xmin}\mspace{45mu} {or}\mspace{14mu} \left( {{{{{{{a_{x} \geq 0}\mspace{14mu}\&}\mspace{14mu} \delta_{wvmin}} \leq {{\overset{.}{\delta}}_{w}} \leq \delta_{wvmax}}\&}{\delta_{w}}} \leq \delta_{wmax}} \right)}} \right)\mspace{31mu}\&}\mspace{14mu} {level}\mspace{14mu} {ground}}\mspace{34mu}\&}\mspace{14mu} s} \leq N} \right)}\left\{ \mspace{14mu} {{{{if}\mspace{14mu} \left( {s = 0} \right)\mspace{31mu} \left\{ {{V_{0} = \begin{bmatrix}v_{0} & 0 \\0 & v_{0}\end{bmatrix}};} \right\} \mspace{14mu} V_{s + 1}} = {V_{s} - {g\frac{{V_{s}\begin{bmatrix}\left( X_{k}^{acc} \right)^{2} & {{- X_{k}^{acc}}Y_{k}^{acc}} \\{{- X_{k}^{acc}}Y_{k}^{acc}} & \left( Y_{k}^{acc} \right)^{2}\end{bmatrix}}V_{s}}{1 + {{\gamma \left\lbrack {X_{k}^{acc}\mspace{14mu} - Y_{k}^{acc}} \right\rbrack}{V_{s}\left\lbrack {X_{k}^{acc} - Y_{k}^{acc}} \right\rbrack}^{T}}}}}};} \right\}} & (24)\end{matrix}$

where g, γ and v₀ are three positive numbers, and the time instant kdenotes the regular time instant and the time instant s is theconditional time instant. Equation (24) is also called the covarianceresetting in the normalized least square algorithm. During deceleration,a similar computation to (22) is conducted.

The pitch gradient and the pitch acceleration coefficient are calculatedusing the 2 by 2 matrix V_(s), and the calculated filtered values X_(k),Y_(k), and U_(k), as in the following for acceleration case

$\begin{matrix}{{if}\mspace{14mu} \left( {{{{{\left( {a_{x} \geq {a_{xmin}\mspace{45mu} {or}\mspace{14mu} \left( {{{{{{{a_{x} \geq 0}\mspace{14mu}\&}\mspace{14mu} \delta_{wvmin}} \leq {{\overset{.}{\delta}}_{w}} \leq \delta_{wvmax}}\&}{\delta_{w}}} \leq \delta_{wmax}} \right)}} \right)\mspace{31mu}\&}\mspace{14mu} {level}\mspace{14mu} {ground}}\mspace{34mu}\&}\mspace{14mu} s} \leq N} \right)} & (25) \\\left\{ \mspace{14mu} {{\begin{bmatrix}\rho_{s + 1} \\\sigma_{s + 1}\end{bmatrix}^{acc} = {\begin{bmatrix}\rho_{s} \\\sigma_{s}\end{bmatrix}^{acc} - {g \frac{{S_{s}\left\lbrack {X_{k}^{acc}\mspace{14mu} - Y_{k}^{acc}} \right\rbrack}^{T}U_{k}}{1 + {{\gamma \left\lbrack {X_{k}^{acc}\mspace{14mu} - Y_{k}^{acc}} \right\rbrack}{S_{s}\left\lbrack {X_{k}^{acc} - Y_{k}^{acc}} \right\rbrack}^{T}}}}}};} \right. & \; \\\} & \;\end{matrix}$

Similar computation for deceleration can be conducted.

The calculated values are also limited to within their feasible sets asin the following for acceleration case

ρ_(s+1) ^(acc)=sat(ρ_(s+1) ^(acc),ρ₀ ^(acc)−Δρ,ρ₀ ^(acc)+Δρ)

σ_(s+1) ^(acc)=sat(σ_(s+1) ^(acc),σ₀ ^(acc)−Δσ,σ₀ ^(acc)+Δσ)  (26)

and the following for deceleration case

ρ_(t+1) ^(dec)=sat(ρ_(s+1) ^(dec),ρ₀ ^(dec)−Δρ,ρ₀ ^(dec)+Δρ)

σ_(s+1) ^(dec)=sat(σ_(s+1) ^(dec),σ₀ ^(dec)−Δσ,σ₀ ^(dec)+Δσ)

During the time instant where the conditions for (24) and (25) do nothold, the computations are frozen to the last values.

From the calculated pitch gradient and the pitch accelerationcoefficient in step 112, the vehicle loading and its distance to thec.g. of the vehicle body in the vertical direction can be determined instep 114.

The variable M_(s) is the nominal vehicle body mass and the distance ofthe initial center of gravity C₀ of the vehicle body from the rear axleis denoted as L which is measured in the longitudinal direction parallelto the vehicle floor (see FIG. 4). If a loading of an additional mass ΔMis added to the trunk or rear portion of the vehicle, and the distancebetween the center of gravity C_(Δ) of this mass and the rear axle isassumed zero, the center of gravity C of the vehicle body with the extramass is likely to change. The longitudinal distance between C₀ and C isΔL. Then

$\begin{matrix}{{\Delta \; L} = {\frac{\Delta \; M}{M_{s} + {\Delta \; M}}L}} & (27)\end{matrix}$

The total pitch inertial of momentum of the vehicle body with respect tothe final (with the added mass) center of gravity C may be expressed as

I _(yc) =I _(yc) ^(M) +I _(yc) ^(ΔM)  (28)

where

I _(yc) ^(M) =I _(yc0) +M _(s) ΔL ²

I _(yc) ^(ΔM) =ΔM( L−ΔL)²  (29)

By plugging (27) into (29), (28) can be expressed as the following

$\begin{matrix}{I_{yc} = {I_{{yc}\; 0} + \frac{M_{s}\Delta \; {ML}^{2}}{M_{s} + {\Delta \; M}}}} & (30)\end{matrix}$

Let the nominal pitch gradient and the pitch acceleration coefficient beρ₀ and or σ₀, then

$\begin{matrix}{{\rho_{0} = \frac{M_{s}h}{K_{pitch}}}{\sigma_{0} = \frac{I_{y}}{K_{pitch}}}} & (31)\end{matrix}$

where K_(pitch) denotes the pitch stiffness due to suspension and itsvalue is different for vehicle deceleration and acceleration. Denotethem as K_(pitch) _(—) _(acc) for acceleration and K_(pitch) _(—)_(dec for deceleration respectively. Then for vehicle accelerating,)

$\begin{matrix}{{\rho_{0}^{acc} = \frac{M_{s}h}{K_{pitch\_ acc}}}{\sigma_{0}^{acc} = \frac{I_{y}}{K_{pitch\_ acc}}}} & (32)\end{matrix}$

and for vehicle decelerating,

$\begin{matrix}{{\rho_{0}^{dec} = \frac{M_{s}h}{K_{pitch\_ dec}}}{\sigma_{0}^{dec} = \frac{I_{y}}{K_{pitch\_ dec}}}} & (33)\end{matrix}$

Using those nominal values and the calculated values ρ^(dec),σ^(dec),and ρ^(acc),σ^(acc), the loading mass and the loading distance satisfythe following for acceleration case

$\begin{matrix}{{{\Delta \; {ML}} = {{K_{pitch\_ acc}\left( {\rho^{acc} - \rho_{0}^{acc}} \right)} = A_{acc}}}{\frac{\Delta \; {MM}_{s}L^{2}}{M_{s} + {\Delta \; M}} = {{K_{pitch\_ dec}\left( {\sigma^{dec} - \sigma_{0}^{dec}} \right)} = B_{dec}}}} & (34)\end{matrix}$

and for deceleration case

$\begin{matrix}{{{\Delta \; {ML}} = {{K_{pitch\_ decc}\left( {\rho^{dec} - \rho_{0}^{dec}} \right)} = A_{dec}}}{\frac{\Delta \; {MM}_{s}L^{2}}{M_{s} + {\Delta \; M}} = {{K_{pitch\_ dec}\left( {\sigma^{dec} - \sigma_{0}^{dec}} \right)} = B_{dec}}}} & (35)\end{matrix}$

Theoretically, (34) and (35) should be the same, but due to numericalerror, a slight difference is possible. For this reason, the averagedvalues will be used

$\begin{matrix}{{A = \frac{A_{dec} + A_{acc}}{2}}{B = \frac{B_{dec} + B_{acc}}{2}}} & (36)\end{matrix}$

From the relationship in (34) or (35) and the average values in (36),the following estimations of the added mass and the position of theadded mass are determined.

$\begin{matrix}\left\{ \begin{matrix}{L = {\frac{B}{2\; A} + \sqrt{{\frac{1}{4}\left( \frac{B}{A} \right)^{2}} + \left( \frac{B}{M_{s}} \right)^{2}}}} \\{{\Delta \; M} = \frac{A}{\frac{B}{2\; A} + \sqrt{{\frac{1}{4}\left( \frac{B}{A} \right)^{2}} + \left( \frac{B}{M_{s}} \right)^{2}}}}\end{matrix} \right. & (37)\end{matrix}$

In step 116 one of the vehicle systems is controlled. The is a safetysystem such one described above such as a roll or yaw stability system,or one of the vehicle body leveling system 70, the headlight adjustmentsystem 72 and the sensor signal compensation block 74.

In step 100 of FIG. 6, a stability control system such as a rollstability control system or a yaw stability control system is controlledin response to the added mass and the height of the added mass. Thesafety system may also be controlled directly from the pitch gradientand pitch acceleration coefficient, both of which may be adaptive. Astability control gain/threshold compensation term may also be generatedbased on the pitch gradient, pitch acceleration coefficient, or theadded trunk mass. The threshold may be changed to allow earlierdeployment if an added mass at a predetermined location is determined insteps 114. The amount of compensation will likely be determinedexperimentally based on the vehicle configuration.

If the vehicle has a significant amount of loading, i.e., the calculatedloading exceeds a threshold P_(max)

ΔM≧P_(max)  (38)

and at the same time the longitudinal distance of the mass exceedsanother threshold L_(max).

L≧L_(max)  (39)

then the vehicle is more prone to oversteer. In this case, the yawstability control gains and the sideslip angle control gains need to beincreased in order to have early activation so as to prevent the vehiclefrom getting into uncontrollable and unstable dynamics. Control gainsare set top the value G_(TLMAX), which are tuned for large trunkloading.

If the vehicle has a significant loading, i.e., ΔM≧P_(max), but theloading is not at the vehicle trunk, that is, the longitudinal distanceof the loading is smaller than a lower threshold L_(min)

L≦L_(min)  (40)

all the gains for the feedback control used for commanding the actuatorsare set to a set of values G_(NTLMAX) tuned for large non-trunkloadings.

If the vehicle has a significant loading, i.e., ΔM≧P_(max), but theloading distance is between the trunk distance and zero, i.e., L isbetween a lower threshold L_(min) (possibly zero) and the high thresholdL_(max),

L_(min)≦L≦L_(max)  (41)

all the gains for the feedback control used for commanding the actuatorsare set to the following values adjusted based on the detected loadingheight as in the following

$\begin{matrix}{G_{L} = {G_{NTLMAX} + {\frac{L - L_{\min}}{L_{\max} - L_{\min}}\left( {G_{TLMAX} - G_{NTLMAX}} \right)}}} & (42)\end{matrix}$

If the vehicle has a loading which is below the maximum allowed loadingP_(max) but above the lower bound of a valid trunk loading P_(min),i.e.,

P_(min)≦ΔM≦P_(max)  (43)

Assume all the nominal gains for feedback (for the vehicle with nominalloading) are denoted as G_(nom), then the control gains will be adjustedbased on the detected loading as in the following

$\begin{matrix}{G_{\Delta \; M} = {G_{nom} + {\frac{{\Delta \; M} - P_{\min}}{P_{\max} - P_{\min}}\left( {G_{TLMAX} - G_{nom}} \right)}}} & (44)\end{matrix}$

The pitch gradient itself can also be directly used to adjust controlgains. If the vehicle has a significant increase of pitch gradient,i.e., ρ≧ρ_(min), then all the gains for the feedback control used forcommanding the actuators are set to the following values adjusted basedon the detected pitch gradient as in the following

$\begin{matrix}{G_{\rho} = {G_{\rho {MIN}} + {\frac{\rho - \rho_{\min}}{\rho_{\max} - \rho_{\min}}\left( {G_{\rho {MAX}} - G_{\rho {MIN}}} \right)}}} & (45)\end{matrix}$

where ρ_(min) is the pitch gradient corresponding to a vehicle withouttrunk loading and ρ_(max), is the pitch gradient corresponding to thevehicle with maximum trunk loading allowed.

Notice that the control gain adjustments other than the above listedlinear interpolation methods are possible. Also, notice that thedead-bands and thresholds used in stability feedback control can also besimilarly adjusted based on the loading distance L and/or the loadingΔM, or the pitch gradient, or the pitch moment of inertia calculated asin (32).

With the added trunk loading, the front and rear normal loadings can becalculated as

$\begin{matrix}{{N_{f} = {N_{f\; 0} + {\frac{{L_{0}\Delta \; M} + {\Delta \; {LM}} + {\Delta \; {LM}}}{b}g}}}{N_{r} = {N_{r\; 0} + {\Delta \; {Mg}} - {\frac{{L_{0}\Delta \; M} + {\Delta \; {LM}} + {\Delta \; {LM}}}{b}g}}}} & (46)\end{matrix}$

where b is the vehicle base, N_(f0),N_(r0) are nominal normal loadingsat the front and rear axle when vehicle does not have trunk loading, L₀is the distance from the nominal c.g. of the vehicle to the rear axle.The nominal loading generated pitch misalignment of the vehicle can becalculated as

$\begin{matrix}{\phi_{{LPM}\; 0} = {\frac{1}{2\; b}\left( {\frac{N_{f\; 0}}{K_{f}} - \frac{N_{r\; 0}}{K_{r}}} \right)}} & (47)\end{matrix}$

where K_(f),K_(r) are the vertical suspension rates for the front andrear axles. For a well-tuned vehicle, such a nominal loading inducedpitch misalignment is usually zero, i.e., φ_(LPM0)=0.

The load induced pitch misalignment caused by the trunk loading can besimilarly computed as

$\begin{matrix}{\phi_{LPM} = {\frac{1}{2\; b}\left( {\frac{N_{f}}{K_{f}} - \frac{N_{r}}{K_{r}}} \right)}} & (48)\end{matrix}$

In 74, the deviation Δφ_(LPM) between φ_(LPM0) and φ_(LPM) can be usedto correct the sensor readings as in the following

ω_(xcorrected)=ω_(x) cos(Δφ_(LPM))−ω_(z) sin(Δω_(LPM))

ω_(zcorrected)=ω_(x) sin(Δφ_(LPM))+ω_(z) cos(Δω_(LPM))

a _(xcorrected) =a _(x) cos(Δφ_(LPM))−a _(z) sin(Δω_(LPM))

a _(zcorrected) =a _(x) sin(Δφ_(LPM))+a _(z) cos(Δω_(LPM))  (49)

where ω_(xcorrected),ω_(zcorrected),a_(xcorrected),a_(xcorrected) arethe corrected roll rate, yaw rate, longitudinal acceleration andvertical acceleration respectively. Notice that from (49), if thevehicle is only yawing without rolling, the roll rate sensor mounted onthe vehicle could still have roll rate output.

The above calculated loading induced pitch misalignment can be fed into70, 72 to achieve the desired control functions.

While particular embodiments of the invention have been shown anddescribed, numerous variations and alternate embodiments will occur tothose skilled in the art. Accordingly, it is intended that the inventionbe limited only in terms of the appended claims.

1. A method of controlling a vehicle system for a vehicle comprising:determining an adaptive pitch gradient; and controlling the vehiclesystem in response to the adaptive pitch gradient.
 2. A method asrecited in claim 1 wherein determining an adaptive pitch gradientcomprises determining the adaptive pitch gradient from a pitch ratesensor signal.
 3. A method as recited in claim 1 wherein determining anadaptive pitch gradient comprises determining the adaptive pitchgradient in response to a longitudinal acceleration signal.
 4. A methodas recited in claim 1 wherein determining an adaptive pitch gradientcomprises determining the adaptive pitch gradient in response to alongitudinal acceleration signal and a pitch acceleration signal.
 5. Amethod as recited in claim 1 wherein determining an adaptive pitchgradient comprises determining the adaptive pitch gradient in responseto a longitudinal acceleration signal, a pitch rate signal and a pitchacceleration signal.
 6. A method as recited in claim 1 whereindetermining an adaptive pitch gradient comprises determining theadaptive pitch gradient in response to a longitudinal accelerationsignal, a pitch rate signal, a pitch acceleration signal, a yaw ratesignal and a relative roll angle.
 7. A method as recited in claim 1wherein controlling the vehicle system comprises adaptively adjusting apitch angle determination in response to the adaptive pitch gradient. 8.A method as recited in claim 1 wherein controlling the vehicle systemcomprises adjusting control gains in response to the adaptive pitchgradient.
 9. A method as recited in claim 1 further comprisingdetermining a pitch acceleration coefficient and wherein controllingcomprises controlling the vehicle system in response to the adaptivepitch gradient and the pitch acceleration coefficient.
 10. A method asrecited in claim 9 wherein the pitch acceleration coefficient isadaptively determined.
 11. A method as recited in claim 9 whereindetermining a pitch acceleration coefficient comprises determining thepitch acceleration coefficient from a pitch rate sensor signal.
 12. Amethod as recited in claim 9 wherein determining a pitch accelerationcoefficient comprises determining the pitch acceleration coefficient inresponse to a longitudinal acceleration signal.
 13. A method as recitedin claim 9 wherein determining a pitch acceleration coefficientcomprises determining the pitch acceleration coefficient in response toa longitudinal acceleration signal and a pitch acceleration signal. 14.A method as recited in claim 9 wherein determining a pitch accelerationcoefficient comprises determining the pitch acceleration coefficient inresponse to a longitudinal acceleration signal, a pitch rate signal anda pitch acceleration signal.
 15. A method as recited in claim 9 whereindetermining a pitch acceleration coefficient comprises determining thepitch acceleration coefficient in response to a longitudinalacceleration signal, a pitch rate signal, a pitch acceleration signal, ayaw rate signal and a relative roll angle.
 16. A method as recited inclaim 1 wherein controlling the vehicle system comprises controlling asafety system.
 17. A method as recited in claim 16 wherein controllingthe safety system comprises controlling a roll stability control system.18. A method as recited in claim 16 wherein controlling the safetysystem comprises controlling a yaw stability control system.
 19. Amethod as recited in claim 1 wherein controlling the vehicle systemcomprises controlling a headlight leveling system.
 20. A method asrecited in claim 1 wherein controlling the vehicle system comprisescontrolling a vehicle body leveling system.
 21. A method as recited inclaim 1 wherein controlling the vehicle system comprises compensating atleast one sensor output.
 22. A method of controlling a vehicle systemfor a vehicle comprising: determining an adaptive pitch accelerationcoefficient; and controlling the vehicle system in response to theadaptive pitch acceleration coefficient.
 23. A method as recited inclaim 22 wherein determining an adaptive pitch acceleration coefficientcomprises determining the adaptive pitch acceleration coefficient from apitch rate sensor signal.
 24. A method as recited in claim 22 whereindetermining an adaptive pitch acceleration coefficient comprisesdetermining the adaptive pitch acceleration coefficient in response to alongitudinal acceleration signal.
 25. A method as recited in claim 22wherein determining an adaptive pitch acceleration coefficient comprisesdetermining the adaptive pitch acceleration coefficient in response to alongitudinal acceleration signal and a pitch acceleration signal.
 26. Amethod as recited in claim 22 wherein determining an adaptive pitchacceleration coefficient comprises determining the adaptive pitchacceleration coefficient in response to in response to a longitudinalacceleration signal, a pitch rate and a pitch acceleration signal.
 27. Amethod as recited in claim 22 wherein determining an adaptive pitchacceleration coefficient comprises determining the adaptive pitchacceleration coefficient in response to a longitudinal accelerationsignal, a pitch rate signal, a pitch acceleration signal, a yaw ratesignal and a relative roll angle.
 28. A method as recited in claim 22wherein controlling the vehicle system comprises controlling a safetysystem.
 29. A method as recited in claim 28 wherein controlling thesafety system comprises controlling a roll stability control system. 30.A method as recited in claim 28 wherein controlling the safety systemcomprises controlling a yaw stability control system.
 31. A method asrecited in claim 22 wherein controlling the vehicle system comprisescontrolling a headlight leveling system.
 32. A method as recited inclaim 22 wherein controlling the vehicle system comprises controlling avehicle body leveling system.
 33. A method as recited in claim 22wherein controlling the vehicle system comprises compensating at leastone sensor output.
 34. A method as recited in claim 22 whereincontrolling the safety system comprises adaptively adjusting a pitchangle determination in response to the adaptive pitch accelerationcoefficient.
 35. A method as recited in claim 22 wherein controlling thesafety system comprises adjusting control gains in response to theadaptive pitch gradient.
 36. A method of controlling a vehicle systemfor a vehicle comprising: determining a pitch gradient; determining apitch acceleration coefficient; determining an added mass and a positionof the added mass from the pitch gradient and the pitch accelerationcoefficient; and controlling the vehicle system in response to the addedmass and position of the added mass.
 37. A method as recited in claim 36wherein determining a pitch gradient comprises determining a pitchgradient from a pitch rate sensor signal.
 38. A method as recited inclaim 36 wherein determining a pitch acceleration coefficient comprisesdetermining a pitch acceleration coefficient from a pitch rate sensorsignal.
 39. A method as recited in claim 36 wherein the positioncorresponds to a change in a center of gravity position.
 40. A method asrecited in claim 36 wherein controlling the vehicle system comprisescontrolling a safety system.
 41. A method as recited in claim 40 whereincontrolling the safety system comprises controlling a roll stabilitycontrol system.
 42. A method as recited in claim 40 wherein controllingthe safety system comprises controlling a yaw stability control system.43. A method as recited in claim 36 wherein controlling the vehiclesystem comprises controlling a headlight leveling system.
 44. A methodas recited in claim 36 wherein controlling the vehicle system comprisescontrolling vehicle body leveling system.
 45. A method as recited inclaim 36 wherein controlling the vehicle system comprises compensatingat least one sensor output.
 46. A method as recited in claim 36 whereindetermining a pitch gradient comprises determining the pitch gradient inresponse to a pitch rate signal and a longitudinal acceleration signal.47. A method as recited in claim 36 wherein determining a pitch gradientcomprises determining the pitch gradient in response to a longitudinalacceleration signal, a pitch rate signal and a pitch accelerationsignal.
 48. A method as recited in claim 36 wherein determining a pitchgradient comprises determining the pitch gradient in response to alongitudinal acceleration signal, a yaw rate signal and a pitch ratesignal.
 49. A method as recited in claim 36 wherein determining a pitchgradient comprises determining the pitch gradient in response to alongitudinal acceleration signal, a pitch rate signal, a pitchacceleration signal and a yaw rate signal.
 50. A method as recited inclaim 36 wherein determining a pitch gradient comprises determining thepitch gradient in response to a longitudinal acceleration signal, apitch rate signal, a pitch acceleration signal, a yaw rate signal and arelative roll angle.
 51. A method as recited in claim 36 whereindetermining a pitch acceleration coefficient comprises determining thepitch acceleration coefficient in response to a pitch rate signal and alongitudinal acceleration signal.
 52. A method as recited in claim 36wherein determining a pitch acceleration coefficient comprisesdetermining the pitch acceleration coefficient in response to alongitudinal acceleration signal, a pitch rate and a pitch accelerationsignal.
 53. A method as recited in claim 36 wherein determining a pitchacceleration coefficient comprises determining the pitch accelerationcoefficient in response to a longitudinal acceleration signal, a yawrate signal and a pitch rate signal.
 54. A method as recited in claim 36wherein determining a pitch acceleration coefficient comprisesdetermining the pitch acceleration coefficient in response to alongitudinal acceleration signal, a pitch rate signal, a pitchacceleration signal and a yaw rate signal.
 55. A method as recited inclaim 36 wherein determining a pitch acceleration coefficient comprisesdetermining the pitch acceleration coefficient in response to alongitudinal acceleration signal, a pitch rate signal, a pitchacceleration signal, a yaw rate signal and a relative roll angle.
 56. Amethod for controlling a vehicle system for a vehicle comprising:sensing a pitch rate; sensing a longitudinal acceleration; sensing a yawrate; determining an input representative of added mass and a positionof the added mass from the sensed pitch rate, the sensed longitudinalacceleration and the sensed yaw rate; and controlling the vehicle systemin response to the input representative of added mass and the positionof the added mass.
 57. A method as recited in claim 56 whereincontrolling the vehicle system comprises controlling a safety system.58. A method as recited in claim 57 wherein controlling the safetysystem comprises controlling a roll stability control system.
 59. Amethod as recited in claim 57 wherein controlling the safety systemcomprises controlling a yaw stability control system.
 60. A method asrecited in claim 56 wherein controlling the vehicle system comprisescontrolling a headlight leveling system.
 61. A method as recited inclaim 56 wherein controlling the vehicle system comprises controllingvehicle body leveling system.
 62. A method as recited in claim 56wherein controlling the vehicle system comprises compensating at leastone sensor output.